This application claims the priority of German Application No. 198 12 236.5, filed Mar. 20, 1998, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a method for suppressing high-frequency oscillations in the steered axles of a vehicle with a regulating device for regulating a steering angle, as is known, for example, from German Patent document DE 42 26 746 A1.
A method is described in German Patent document DE 43 25 413 A1 that makes it possible to calculate in a computer a steering angle that depends on a driving situation. A setpoint of the steering angle is calculated on the basis of the steering wheel angle produced by the driver using the steering wheel as an actuating means, as well as the yaw angle rate as a value that characterizes the driving behavior.
Active steering of this type has the advantage that the range of driving states that can be controlled within the framework of what is physically possible is expanded. However, the disadvantage is that as a result of the regulation of the steering angle, the steering stiffness, and the running-in behavior of the wheel, high-frequency oscillations of the wheel around its vertical axis result. The occurrence of these oscillations is termed the "shimmy" effect.
The development of this "shimmy" effect could be counteracted by low-pass filters for the setpoint of the steering angle. However, this has the disadvantage that the bandwidth of the regulation of the steering angle and therefore its regulating quality deteriorate. Regardless of the regulation of the steering angle, the high-frequency oscillations can also be excited by the actuation of the brake.
The goal of the invention is to reliably prevent the occurrence of the shimmy effect while at the same time not adversely affecting the regulating quality of the steering angle.
This goal is achieved using a regulating system for the steering angle in order to perform a method for suppressing high-frequency oscillations in the steered axles of a vehicle. The regulating device at the steered axle acts to regulate a steering angle as a function of a setpoint (.delta..sub.S) that has been calculated. With a computer in which, in a setpoint calculator, on the basis of (1) a steering wheel angle specified at an actuating means by the driver; and (2) at least one value characterizing the driving behavior of the vehicle, the setpoint is determined for the steering angle and supplied to the regulating device. A value for the steering rate is determined in the computer on the basis of a model for the steering and is supplied to the setpoint calculator as an additional input value.
A setpoint for the steering angle is fed to a regulating device. The regulating device regulates the setpoint at the steered axle associated with it. The setpoint is calculated in a computer, and in addition to the steering angle specified by the driver and values that characterize driving behavior, a value of the steering rate calculated on the basis of the model of the steering is supplied as input values.
According to embodiments of the invention, the lateral force on the steered wheels and/or the setpoint of the steering angle are used to calculate the steering rate. In another embodiment of the invention, the steering acceleration can be calculated in addition to the steering rate and supplied to the setpoint calculator.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.